This will be the seventh in a series of Gordon Conferences on muscle contraction which began in 1966 under the auspices of the Cardiac Muscle Society. The 1975 conference will deal with the contraction mechansim itself. The conference will focus mainly on skeletal muscle, because the structural and biochemical characteristics of this tissue make it particularly suitable for studying the properties of the cross- bridge mechanism. However, the results will be of very general interest because the cross-bridge mechanism is essentially the same in skeletal, cardiac, and smooth muscle; in addition, a very similar mechanism appears to underlie all forms of cell motility. The conference will bring together a variety of different approaches: mechanical studies, which give information about cross- bridge "reach" and the rate constants for cross bridge turnover; biochemical studies, which reveal the properties of the proteins directly involved in contractile activity, as well as those which regulate this activity; and structural studies, which elucidate the conformational changes associated with cross-bridge activity. Within the framework of the conference, there will be a great deal of interchange between investigators in the skeletal and cardiac areas (smooth muscle was covered in the 1973 Conference). There will also be ample opportunity for discussion between investigators of basic phenomena and workers who are more clinically oriented. Topics of particular clinical relevance include the polymorphism of myofibrillar proteins which may be a factor in certain muscular diseases, and the influence of protein phosphorylation on the regulation of contractile activity. Several of the proposed conference sessions focus on very recent advances in muscle research which have not been previously discussed in similar meetings. For this reason, it should be particularly advantageous to have a conference in a setting which favors free and informal exchange of ideas between a wide range of scientists whose common interest is the cross-bridge contraction mechanism.